Ineffective thermal communication between a heat source and a heat sink can hamper the dissipation of excess heat from a system. Heat spreaders represent one approach for thermal management that can be employed in many instances. Heat spreaders can promote more effective thermal communication between a heat source and a heat sink by distributing concentrated heat from a dimensionally small heat source to a considerably larger area at the heat sink. Most typically, a heat spreader abuts both a heat source and a heat sink, thereby providing a continuous bridge through which heat can pass. By spreading the heat over a larger dimensional area at the heat sink, materials having a greater breadth of thermal tolerance can be employed than if the heat remains concentrated in a smaller area. Alternately, a heat spreader can provide a more effective geometry for heat dissipation to take place at the heat sink than would otherwise be possible.
Heat spreaders can be used in a variety of thermal management settings. In some cases, dissipation of excess heat from a system can protect various system components from damage due to overheating. Heat spreaders can often be used for this purpose in the microelectronics industry to protect processing elements and other circuitry from thermal damage. In other cases, dissipation of excess heat from a system can promote more efficient operation of various system components. As a specific example, the performance of communication systems in space vehicles and other environments can be strongly influenced by the thermal state of solid state power amplifiers (SSPAs) housed therein. It can often be difficult to distribute high power densities residing on the power amplifier into large-area radiators for rejection of waste heat into space. Although heat spreaders can facilitate these processes and others, they can often be limited in their effectiveness at doing so, as discussed hereinafter. Moreover, it is considered unlikely that present heat spreader technologies can accommodate the rate of power density increase currently ongoing in electronic devices.
Existing heat spreader technologies often use metals such as copper or aluminum, alloys such as WCu or MoCu, ceramics such as SiC or BN, phase change materials, BeO, diamond, graphite, pitch-based carbon fiber composites, copper graphite composites, and/or thin sheets of highly oriented pyrolytic carbon as conductive materials to promote heat conduction. In their present forms, heat spreaders based upon these conductive materials often suffer from shortcomings ranging from insufficient thermal conductivity, purely isotropic thermal properties, overly anisotropic thermal properties, effectiveness only as thin layers, brittleness at low operating temperatures (below about −20° C.), high densities and weights, extended processing times, and/or high processing temperatures (>1000° C.) and pressures (>1 GPa). It can oftentimes be difficult to establish good thermal contact of a heat spreader to a heat source and/or a heat sink, leading to further thermal management difficulties. In addition to inadequate thermal performance, the foregoing factors can lead to application-specific incompatibilities such as, for example, unacceptable mechanical performance and/or poor payload economics due to excessive weight. Further, extreme processing conditions and excessive processing times can represent an undesirable cost burden in some instances.
As indicated above, purely isotropic or overly anisotropic heat conduction can be problematic for heat spreader technologies. Substantially isotropic heat conduction can result in inadequate lateral distribution of heat and generation of excessive “hot spots” at the heat sink, which can be damaging and also result in poor heat transfer, especially when heat is being transferred to a heat pipe system. Overly anisotropic heat conduction can likewise be problematic. Anisotropic through-plane heat conduction can similarly result in generation of “hot spots” and poor lateral distribution of heat. Overly anisotropic in-plane (i.e., lateral) heat conduction, in contrast, can result in poor conveyance of heat to a heat sink.
It can be difficult to achieve a thermal conductivity profile that is sufficiently anisotropic to allow lateral heat conduction to take place while still achieving good through-plane heat transfer. In their present forms, copper and aluminum provide excessively high through-plane heat transfer. CVD diamond similarly provides high thermal conductivity in the through-plane direction and minimal lateral heat distribution. Although graphite can distribute heat laterally, it can exhibit overly anisotropic heat transfer performance and can be difficult to employ on a large scale. Moreover, graphite cannot typically be brazed or soldered to establish a direct bond to a heat source or a heat sink. Metal epoxies and metal-fiber composites can similarly be limited by their low thermal conductivity values and/or high processing temperatures that can degrade mechanical properties.
In view of the foregoing, further improvements in heat spreader technologies and methods for their fabrication would be of significant interest in the art. The present disclosure satisfies these needs and provides related advantages as well.